Feb. 15, 2002
     Prostate Cancer

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PET tracer detects early prostate cancer

SEATTLE -- Feb. 16, 2002 (Cancer Digest)-- A new imaging agent may help doctors more accurately diagnose prostate cancer in the early stages of disease. The new agent is a radioactive tracer that is more readily taken up by prostate cancer cells to produce a better x-ray image.

The research team led by Dr. Nobuyuki Oyama of Japan's Fukui Medical University, Fukui, compared two different radiotracers used with high-energy x-ray scan, called positron emission tomography, or PET scan for 18 patients with prostate cancer confirmed by biopsy.

The results of the small study showed that 100% of patients scanned using the tracer called 11C-acetate were positive for primary prostate cancer, while only 83% of those scanned with the standard tracer 18F-FDG were positive.

The tracer 11C-Acetate not only showed significantly greater sensitivity for prostate cancer, it was also better able to detect the spread (metastasis) of the cancer to distant parts of the body. The researchers concluded that 11C-acetate PET imaging may be able to detect prostate cancers that are currently undetectable by 18F-FDG PET.

PET scans are an imaging method using a radioactive material that is taken up by cells that are actively processing glucose throughout the body. A patient undergoing a PET scan is injected with the fluorodeoxyglucose (FDG) approximately 45 minutes before the scan. The glucose tracer emits signals that are picked up by the PET scanner.

Fast-dividing cancer cells take up more of the radioactive material than other cells thus making small tumors show up that are not detected by other imaging techniques.

A computer reassembles the signals into images that display the distribution of metabolic activity in the body. Areas in which cancer is present will show up more brightly on the scan because the disease is more metabolically active than noncancerous cells.

Unfortunately, 18F-FDG PET has not proven effective in detecting early prostate cancer. This is because the18F-FDG (fluorodeoxyglucose) tracer is not taken up well by prostate tumors, which often have a slower glucose metabolism. 11C-Acetate also responds to metabolic activity, but how or why it has higher uptake within prostate tumors is not clear.

Prostate cancer is the most common cancer in men, and the second leading cause of cancer deaths in men over 40 in the United States. PET scans using various tracer elements have been increasingly recognized as a vital tool in the diagnosis of many cancers, including melanoma, lymphoma, and lung, colorectal, and breast cancer.